It is known to provide a surgical jig having a cutting guide, which assists a surgeon in making accurate and repeatable cuts during surgery. The accuracy of a cut made using a cutting guide is mainly determined by the successful positioning and fastening of the cutting guide in the operative area. Typically, a stylus is attached to the cutting guide, which references from a reference point or marker on the body, for example, a bone. The stylus is either free to translate and/or rotate relative to the cutting guide, so that it may be adjusted, or is rigidly fixed to the cutting guide. An attachment mechanism mounts the stylus to the cutting guide, and a locking mechanism locks the stylus in a desired position relative to the attachment mechanism and hence the cutting guide. Once in the operating position, the jig can be attached to, for example, a bone using pins and/or bone screws.
The use of a stylus to position a cutting guide is common in joint replacement surgery. For example, during a total or partial knee replacement operation, it is necessary to resect the proximal tibia to a specific level. Existing tibial styli reference from the tibial plateau. This area of the joint is subject to considerable wear and, in a knee requiring joint replacement is likely to be damaged. Therefore, the tibial plateau does not provide a reliable reference position. It is desirable to provide a stylus assembly that enables referencing from an area of undamaged bone, which would provide a more reliable reference position.
Once a stylus has been used to position a cutting guide, the stylus is usually removed, in order to increase the working space available to the surgeon. A problem of existing arrangements is that the removal of the stylus can cause unintentional and unnoticed movement of the cutting guide. This leads to inaccurate positioning of the cutting guide, with the result that the surgeons' incisions are misdirected. It is therefore also desirable to provide a stylus assembly which can be removed with the minimum of handling.